Explain disadvantages of conventional file-based system compared to Database Management System.
Disadvantage of conventional file-based system are:
Data Redundancy
- It is possible that the same information may be duplicated in different files. This leads to data redundancy.
- Data redundancy results in memory wastage.
- For example, consider that some customers have both kinds of accounts - saving and current. In this case, data about customers - name, address, e-mail, contact number - will be duplicated in both files, file for saving accounts and file for current accounts. This leads to requirement of higher storage space. In other words, same information will be stored in two different locations (files). And, it wastes memory.
Data Inconsistency
- Due to data redundancy, it is possible that data may not be in consistent state.
- For example, consider that an address of some customer changes. And, that customer has both kinds of accounts. Now, it is possible that this changed address is updated in only one file, leaving address in other file as it is. As a result of this, same customer will have two different addresses in two different files, making data inconsistent.
Difficulty in Accessing Data
- Accessing data is not convenient and efficient in file processing system.
- For example, suppose, there is a program to find information about all customers. But, what if there is a need to find out all customers from some particular city. In this case, there are two choices here: One, find out all customers using available program, and then extract the needed customers manually. Second, develop new program to get required information. Both options are not satisfactory.
- For each and every different kind of data access, separate programs are required. This is neither convenient nor efficient.
Limited Data Sharing
- Data are scattered in various files.
- Different files may have different formats. And these files may be stored in different folders (directories) may be of different computers of different departments.
- So, due to this data isolation, it is difficult to share data among different applications.
Integrity Problems
- Data integrity means that the data contained in the database is both correct and consistent. For this purpose, the data stored in database must satisfy certain types of constraints (rules).
- For example, a balance for any account must not be less than zero. Such constraints are enforced in the system by adding appropriate code in application programs. But, when new constraints are added, such as balance should not be less than Rs. 5000, application programs need to be changed. But, it is not an easy task to change programs whenever required.
Atomicity Problems
- Any operation on database must be atomic. This means, operation completes either 100% or 0%.
- For example, a fund transfer from one account to another must happen in its entirely. But, computer systems are vulnerable to failure, such as system crash, virus attack. If a system failure occurs during the execution of fund transfer operation, it may possible that amount to be transferred, say, Rs. 500, is debited from one account, but is not credited to another account.
- This leaves database in inconsistent state. But, it is difficult to ensure atomicity in a file processing system.
Concurrent Access Anomalies
- Multiple users are allowed to access data simultaneously (concurrently). This is for the sake of better performance and faster response.
- Consider an operation to debit (withdrawal) an account. The program reads the old balance, calculates the new balance, and writes new balance back to database. Suppose an account has a balance of Rs. 5000. Now, a concurrent withdrawal of Rs. 1000 and Rs. 2000 may leave the balance Rs. 4000 or Rs. 3000 depending upon their completion time rather than the correct value of Rs. 2000.
- Here, concurrent data access should be allowed under some supervision.
- But, due to lack of co-ordination among different application programs, this is not possible in file processing systems.
Security Problems
- Database should be accessible to users in a limited way.
- Each user should be allowed to access data concerning his application only.
- For example, a customer can check balance only for his/her own account. He/She should not have access for information about other accounts. But, in file processing system, application programs are added in an ad hoc manner by different programmers. So, it is difficult to enforce such kind of security constraints.
